I am doing some refurbing on my entire dash and cluster assembly, and as I come across certain items that I think are pertinent to everyone, I post up on them.

This one is about speedometers, thier cables and maintenance for them.

First of all, if yours is working correctly...don't "improve" it. Only work on it if there is a clear need.

If the needle is a little jumpy or twitchy, you may have either a slight kink in the cable, or a cable in need of some lubricant.

Check to make sure the cable is smooth with no bends, a nice gentle arc.

Assuming you havent moved the cable recently, it probably is not that.

If you feel you need to lube the cable, simply pull the cable out of the tube from the top end. Ford used a chicken-shit method of making thier speedo cables back then that did not require precision lengths of the cables. Many of them have a plastic grommet-like contraption on the end, and if those are smashed or destroyed from previous repeated removals and reinstallations, you may need a new cable.
But, to lube the cable: some have a brass clip that holds the cable in the sheath, others don't. Figure yours out, and then slowly remove the cable.
To lube it, put a LITTLE BIT of wheel bearing grease on the cable, slide it in a ways, put a LITTLE more grease on, slide in some more, a LITTLE more grease, etc...
The key, obviously is to use VERY LITTLE grease.
When you get close to the upper end, do not put grease on this area...you may not get the cable to fully seat and clip onto the speedo head otherwise.
Once you get the cable all the way back in, give it a little twist until the other end drops a bit further into the transmission gear.
Then just reattach to your speedo unit.

A word of caution: DO NOT under any circumstances use WD-40 or any other kind of spray lubricant on the cable, in the tube, or anywhere on the speedometer assembly.
I have seen several instances where soneone did so, and the spinning cable worked the oil back up and out of the tube and onto some electrical components and caused a fire in the dash. Nobody wants that.
The speedometer head does not require any lubricant in it ever, so don't do it.